Cocrystallization in random copolymers of poly(β-hydroxybutyrate-co-β-hydroxyvalerate) and its effect on crystalline morphology

Abstract

Small-angle X-ray scattering (SAXS) and solid state CPMAS I3c NMR were used to describe the crystalline morphology of a series of bacterially produced poly((3-hydroxybutyrate-co-P-hydroxyvalerate) copolymers containing random distributions of 3-hydroxybutyrate (3HB) and 3-hydroxyvalerate (3HV). Modeling of SAXS results showed that the morphology of this isodimorphic system is better described by two phases, crystalline and amorphous, having defects within each domain. This is in contrast to a model with a large interfacial region between phases. For the 3HV composition range 0-27 mol%, the polymer crystallizes in a poly(P-hydr0xybutyrate)-type crystalline lattice. Solid state NMR results showed that there is significant incorporation of the 3HV minor component into the poly(P-hydroxybutyrate) crystalline phase over this composition range. The ratio of the 3HV content in the crystalline phase relative to the overall 3HV content is not linear, but increases with increasing 3HV. For the 21 and 27% 3HV samples, the 3HV content in the crystalline phase is as much as 213 of the overall 3HV content. Inclusion of 3HV is correlated to an increase in crystalline disorder (as measured by SAXS), implying that it is easier to accommodate the bulkier 3HV comonomer into a crystalline region that already contains defects.Key words: bacterial polyesters, poly(3-hydroxyalkanates), small-angle X-ray scattering, solid state NMR, cocrystallization.RCsumC : On a utilisC la diffraction des rayons X B de petits angles (SAXS) et la RMN du 13c CPMAS B 1'Ctat solide pour dCcrire la morphologie cristalline d'une sCrie de copolymkres poly(P-hydroxybutyrate-co-phydroxyvalCrate) produits par une voie bactCrienne et contenant des distributions au hasard de 3-hydroxybutyrate (3HB) et de 3-hydroxyvalCrate (3HV). Un modelage des resultats SAXS a montrC que la meilleure f a~o n de dCcrire la morphologie de ce systkme isodimorphique est B l'aide de deux phases, l'une cristalline et l'autre amorphe, ayant des dkfauts dans chaque domaine. Pour une composition de 3HV allant de 0 i 27 mol%, le polymkre cristallise dans une rCseau cristallin du type poly(P-hydroxybutyrate). Les rCsultats de la RMN B l'etat solide ont montrC que, sur cette plage decomposition, il se produit une incorporation importante du composant mineur du 3HV dans la phase cristalline du poly(P-hydroxybutyrate). Le rapport de la quantitC de 3HV contenue dans la phase cristalline par rapport B la quantitC totale de 3HV n'est pas linCaire; il augmente avec une augmentation du 3HV. Pour les Cchantillons contenant 21 et 27% de 3HV, la quantitC de 3HV contenue dans la phase cristalline reprksente pratiquement les 213 de la quantitC totale de 3HV. I1 existe une corrClation entre l'inclusion du 3HV et l'augmentation du dCsordre cristallin (tel que mesurC par SAXS); ceci implique qu'il est plus facile d'accommoder le gros comonombre 3HV dans une region cristalline qui contient dCjB des dCfauts.

The chemomechanical properties of microbial polyhydroxyalkanoates

“…When the 3HV comonomers are included in the P(3HB)type lattice, they will result in "less-perfect" crystals with more defects, smaller crystalline domains and less brittleness [215]. At higher HV contents the spherulites are small as the rate of crystallization is slower and/or there are relatively more nucleation sites.…”

Direct Observation of Stereodefect Sites in Semicrystalline Poly(lactide) Using 13C Solid-State NMR

“…In polyolefins such as isotactic polypropylene, defect sites are generated during the polymerization process, making it impossible to specify which monomer unit will become a defect site. For this reason, most studies of defect sites in polymers have used copolymers, in which the minor component in the copolymer corresponds to a defect site that can readily be identified in the NMR spectrum. − However, defect sites in copolymers are constitutional defects, not configurational defects as found in stereoregular polymers . Another approach to study defect sites is to predict their chemical shifts based upon ab initio calculations and compare the simulated NMR spectrum to the experimental spectrum. , The presence of stereodefects is inferred by their effect on the line shape, but this method requires extensive deconvolution of the line shape into multiple peaks.…”

Origin of the double melting peaks of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) with a high HV content as revealed by in situ synchrotron WAXD/SAXS analyses

“…The two monomers HB and HV are similar in chemical structure, and have the same chain conformation of the left‐handed 2 1 helix in orthorhombic unit cell . The occurrence of isomorphism in P(HB‐ co ‐HV) has been confirmed by wide‐angle X‐ray diffraction (WAXD), nuclear magnetic resonance (NMR), and infrared spectroscopy . Moreover, the crystallization behavior of P(HB‐ co ‐HV) was also affected dramatically by HV content.…”

“…In particular, it has been reported that both the unit cell parameters a and b enlarge with increasing HV content, for the ethyl side group of HV units expands both the planes perpendicular to chain axis . Further, both the percent of HV units in PHB crystals and the disorder of chain folding in crystalline phase increase with HV content . More importantly, the P(HB‐ co ‐HV) with HV content lower than 10 mol % reflects the similar morphological variation to that of PHB, but differs with those of HV content higher than 10 mol % .…”